1. Field of the Invention
This invention relates to lubricating oil compositions, particularly to lubricating oil compositions useful as functional fluids in systems requiring coupling, hydraulic fluids and/or lubrication of relatively moving parts. More particularly, it is concerned with functional fluids for use in the lubrication of heavy machinery, particularly high-power-output tractors, and to the reduction of brake chatter therein.
2. Description of the Prior Art
The use of heavy machinery, such as a tractor, has increased the demand for high-performance lubricating compositions. Modern tractors have many power-assisted components, such as power steering and power brakes. Power brakes are preferably of the disc type since they have greater braking capacity. The preferred disc brakes are the wet-type brake, which are immersed in a lubricant and are therefore isolated from dirt and grime.
Such brakes suffer from at least one problem, namely, brake chatter or brake squawk. This phenomenon is a very unpleasant noise that occurs upon application of the brake. In the past, friction-modifying agents, such as dioleylhydrogen phosphite, have been added to the brake lubricating composition to reduce the chatter. Lubricating compositions containing this additive tend to suffer from very high wear rates, particularly at high temperature.
A further complication in eliminating brake chatter is the desire to use the same functional fluid, not only for the brake lubrication, but also for lubrication of other tractor parts, such as the hydraulic and mechanical power take-offs, the tractor transmission, gears and bearings, and the like. The functional fluid must act as a lubricant, a power transfer means, and as a heat transfer medium. Obtaining a compounded fluid to meet all of these needs without brake chatter is difficult.
U.S. Pat. No. 3,649,538 discloses and claims a process for lubricating aluminum in an aluminum-shaping operation with a lubricant comprising a mineral oil and 0.1 to 30 volume % of a C.sub.10 -C.sub.30 1,2-diol.